1. Field of the Invention
The present invention relates to a nerve stimulation device for stimulating the phrenic nerve of a living subject.
2. Description of the Prior Art
A number of different methods exist for treatment of breathing difficulties. Positive pressure ventilation using a ventilator or respirator is probably the most common method today. It has in principle completely replaced negative pressure ventilation (for example, the iron lung). Stimulation of breathing musculature and the stimulation of nerves related to breathing (especially the phrenic nerve) are known but, in practice, are not used to any great extent.
Various systems for nerve stimulation are described in, for example, PCT Application WO 97/38751 and U.S. Pat. No. 6,360,740. These primarily describe electrical stimulation but it also is known to use magnetic stimulation in order to stimulate nerves.
Nerve stimulation makes heavy demands on functionality to make it as safe and as reliable as possible. The phrenic nerve, for example, is situated near the vagus nerve. Stimulation of the vagus nerve can lead to a slowing of heart activity (bradycardia). Transcutaneous stimulation therefore requires sensitivity in the placement of the electrode, so that only the phrenic nerve is stimulated. A subcutaneous connection to the phrenic nerve, of course, does not present this problem, but a surgical intervention is necessary. Moreover, it is not a simple matter to isolate the phrenic nerve with a surgical intervention. As with all surgical interventions there is the risk that surrounding tissue or nerves will be damaged or affected.
Another problem with nerve stimulation is the choice of stimulation energy necessary to achieve a sufficient response in the musculature of the breathing system (with stimulation of the phrenic nerve it is primarily the diaphragm that is involved).
It would be an advantage if a method of nerve stimulation could be developed in which a physiologically more natural effect resulted and with fewer negative side effects on the patient than with positive pressure ventilation.